A composite of copper grown on the surface of CNTs has been fabricated by a redox reaction between copper acetate and ethylene glycol for use as negative electrode at high currents in electrochemical energy storage. Subsequently, the as-prepared Cu/CNT composite was coated with carbon using glucose as carbon source. Structure, morphology and electrochemical performance of the composite were investigated by scanning electron microscopy, X-ray diffraction, XPS, and electrochemical measurements. The carbon coating effectively prevents the dissolution of copper carbonate complexes formed during the electrode reactions Cu 2 (OH) 2 CO 3 + 2e − → ← Cu 2 O + OH − + HCO − 3 and Cu 2 O + H 2 O + 2e − → ← 2Cu + 2OH − , increases the conductivity of the copper constituent in the negative electrode and protects this component against direct contact with the electrolyte solution during cycling. The C/Cu/CNTs composite exhibits higher capacity and better rate behavior as well as excellent cycling stability in 0. Electrochemical energy storage and conversion systems including batteries, fuel cells, and supercapacitors have attracted considerable attention in recent years since they can improve efficient use of electric energy, and thus reduce emission of greenhouse gases and promote the use of renewable energy.1 A main function of electrochemical capacitors (ECs, most popular called supercapacitors, regarding confusing terminology see Ref.2) is complementing batteries and fuel cells because of their high power capability, they also can provide necessary additional power for acceleration and can store energy during braking in hybrid electric vehicles.3 On a larger scale they can assist in maintaining power quality, 4-8 on a smaller scale they can provide additional power for short periods of time in mobile devices. Thus supercapacitor technology is regarded as a promising means for storing electricity.9 Because frequently materials are employed both in secondary batteries and supercapacitors (on the merger of these fields see Ref. 10,11) 21 All batteries based on pure metals as negative electrode have much higher theoretical capacities because of the smaller atomic weight of elements compared to their corresponding oxides which are frequently employed both in batteries and supercaps (for an overview see Ref.2), according to the equation C = (F · n)/(3.6 M) (C, F, n and M refer to capacity, Faraday constant, number of transferred electrons per unit and atomic/molecular mass, respectively).
22However, most of them -in particular copper -were not investigated in electrochemical capacitors except for a few reports on copperinfiltrated carbonized wood monoliths, 23 cuprous oxide microspherenanosheets, 24 copper-coating of activated carbon used as electrode material in a Li-ion capacitor, 25 copper-doped metal oxides 26 and copper as substrate 27 demonstrating electrochemical activity of copper in alkaline electrolyte solution. Furthermore, copper is a promising candidate electrode material for high power energy storage because of its...
